The research described in this summary is relative to 20 years of mechanical pulp sludge (sludge) utilization research which was initiated in 1992 under the auspices of the Alberta Research Council (ARC) (now part of Alberta Innovates - Technology Futures (AITF)) and Alberta Newsprint Company (ANC) Joint Research Venture and was continued with financial support from the Mechanical Pulp and Paper Consortium Research Program (ANC, Millar Western Forest Products – Pulp Division (Millar) and Slave Lake Pulp (SLP)). The Mechanical Pulp and Paper Consortium ‘Sludge Utilization’ program emphasized the short-and long-term economic benefits of pulp mill sludge spreading as well as the response to regulatory concerns and the development of operational landspreading guidelines. Sludge utilization was extensively evaluated through experimentation on agricultural and forest soils to determine the most appropriate uses for the material. In an effort to reduce their environmental footprint, economic costs, and enhance local agricultural crop productivity ANC, Millar, and SLP initiated the effort required to get the Standards and Guidelines for the Land Application of Mechanical Pulp Mill Sludge to Agricultural Land approved through Alberta Environment. These guidelines were approved in 1999, and allowed mills to apply a substantial portion of their sludge to local agricultural land.
The pulp and paper consortium has completed over 20 years of research and contributed millions of dollars to determine the best practices for sludge utilization. This document summarizes the results of the sludge utilization research to date. The information summarized in this document was structured to ensure the pulp and paper industry has a comprehensive understanding of the work completed from the early nineties to present. The document is divided into 4 categories based on the application of the work completed and an extended reference list of the reports generated under the Mechanical Pulp and Paper Consortium is provided. The report is categorized by initial characterization work, sludge utilization for agriculture, sludge utilization in the forest and other research relative to sludge.
The initial characterization work began in 1992 to develop a technology for utilization and/or disposal of pulp mill sludge generated at the operations of ANC in an environmentally acceptable manner. The objective of the work was to be met by completion of a review of the relevant North American and European literature pertinent to utilization/disposal of conventional and de-ink sludge; characterization of the conventional and de-ink sludge produced at the operations of ANC to identify parameters that might be beneficial or detrimental in terms of disposal by landspreading; greenhouse pot trials to determine the impact of conventional and de-ink sludge materials on soils and plants and to determine potential landspreading rates; and column leaching studies to determine the leachability of compounds from the conventional and de-ink sludge simulating a landspreading (application/ incorporation) and stockpiling or landspreading without incorporation approach. A human health study was also conducted to determine microbial populations in sludge and their persistence over time with respect to land application.
Agricultural plot trials were established in 1992 to evaluate the impact of single and multiple applications of sludges from different mills to obtain long term data relative to the impact on crop yields and soil quality. Various application rates and techniques were evaluated in addition to storage handling procedures. Sludge was also evaluated as a fertilizer replacement in terms of yield and economics. Operational landspreading on farm fields began in 1993 and was extensively monitored until 1999 when the Guidelines were approved.
Sludge utilization in the forest was initiated with a landspreading field trial involving forest cut-block field locations to determine the impact of different application rates of the conventional and de-ink sludge on soils and trees in 1993. Subsequent trials involved sludge application on juvenile trees, seedling/sucker trials, spreading sludge without incorporation on various slope and aspect positions, sludge application on frozen and frozen and snow covered soils, thinning trials, operational spreading trials and equipment evaluation. To compare the growth response of the different treatments several techniques were used including height and diameter comparisons and projections, survival rates, the age-shift method, which quantifies how much sooner a particular size is reached due to the treatment effect, and growth multipliers, which represent the treatment effect as the ratio of treated to untreated. To compare all treatments,. age shift and growth multiplier calculations were conducted based on a stand age of 25 years and 2000 stems/ha.
Other research relative to mechanical pulp sludge has included reclamation of a disturbed forest road, an abandoned gravel pit, and coarse textured soils at a mill site. In addition, sludge utilization has been evaluated for alpine reclamation, hydrocarbon remediation and composting. The carbon benefits of sludge utilization have also been evaluated for agricultural and forest applications. Quantification protocols were written for the Alberta Offset System detailing enhanced carbon sequestration as a result of sludge land application.
Many widespread conclusions and recommendations have resulted from the sludge utilization program. Some of the general recommendations for sludge utilization include:
- Mechanical pulp mill sludge is beneficial for improving the porosity and tilth of fine textured matrices, enhances moisture holding capacity of coarse textured soils, provides long sustaining nutrient supplies to plants, and can be safely used for agriculture, or to enhance forest productivity in marginal areas.
- Sludge application rate will vary depending on the characteristics of the site and the receiving soil.
- Agricultural and reclamation receiving sites should be relatively dry to ensure incorporation is done effectively and compaction is minimized and the mixing depth for sludge incorporation should not exceed 25 to 30 cm to ensure plant nutrient availability and enhanced rooting zones.